Solving mold filling imbalances in multi-cavity injection molds

It has previously been reported that significant flow and thermal imbalances are developed in the naturally, or geometrically, balanced runner systems typically used in injection molding (1). These imbalances can mean that as much as 95% of the melt can flow to inner cavities in an eight cavity naturally balanced runner system. This paper presents a solution to these flow imbalances through a means of flipping and rotating the melt in the runner. The use of the melt flipping technique developed in the study creates a thermal, flow and material property balance to all cavities, thereby improving product quality and productivity. This paper also expands on previously reported findings to include imbalance test results on additional plastic materials. A study has been conducted to determine which material characteristics contribute to the imbalances and variations for runner and mold layouts that are susceptible to the impact of these flow imbalances.